Creating a custom widget with PyQt

Python PyQt Basic: Exercise-6 with Solution

Write a Python program to create a custom widget by subclassing QWidget using PyQt. This widget should have a unique appearance or behavior.

Note:
The QWidget class is the base class of all user interface objects.

From doc.qt.io:

QApplication Class: The QApplication class manages the GUI application's control flow and main settings.

QWidget: The QWidget class is the base class of all user interface objects.

Qt module: PyQt5 is a set of Python bindings for the Qt application framework. It allows us to use Qt, a popular C++ framework, to create graphical user interfaces (GUIs) in Python.

QPainter Class: The QPainter class performs low-level painting on widgets and other paint devices.

QColor Class: The QColor class provides colors based on RGB, HSV or CMYK values.

Sample Solution:

Python Code:

import sys
from PyQt5.QtWidgets import QApplication, QWidget
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QPainter, QColor
import random

class ColoredCircleWidget(QWidget):
    def __init__(self):
        super().__init__()

        # Set initial properties
        self.circle_color = QColor(255, 0, 0)  # Red
        self.setAutoFillBackground(True)

    def mousePressEvent(self, event):
        # Change the circle's color when clicked
        self.circle_color = QColor(
            random.randint(0, 255),
            random.randint(0, 255),
            random.randint(0, 255)
        )
        self.update()  # Trigger a repaint

    def paintEvent(self, event):
        # Paint the colored circle
        painter = QPainter(self)
        painter.setBrush(self.circle_color)
        painter.setPen(Qt.NoPen)

        width = self.width()
        height = self.height()

        # Ensure the circle fits within the widget
        radius = min(width, height) // 2

        painter.drawEllipse(
            (width - 2 * radius) // 2,
            (height - 2 * radius) // 2,
            2 * radius,
            2 * radius
        )

def main():
    # Create a PyQt application
    app = QApplication(sys.argv)

    # Create an instance of the ColoredCircleWidget
    widget = ColoredCircleWidget()
    widget.setWindowTitle("Custom Widget: Colored Circle - Click on it")

    # Set the widget's size
    widget.setGeometry(100, 100, 300, 300)

    # Show the widget
    widget.show()

    # Run the application's event loop
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Explanation:

In the exercise above -

• Import the necessary modules.
• Create a custom widget ColoredCircleWidget by subclassing 'QWidget'.
• Initialize the widget with 'red' as the initial circle color.
• The mousePressEvent method is overridden to change the circle's color when the widget is clicked. Additionally, the appearance is updated by repainting.
• The "paintEvent()" method is overridden to paint the colored circle using a 'QPainter'.
• Finally start the application's event loop.

Output:

Flowchart:

Python Code Editor:

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